(1) Field of the Invention
The present invention relates to the removal of deleterious materials from a liquid, especially water, and particularly to the conditioning of water prior to its delivery to a steam generator. More specifically, the present invention is directed to a water conditioning system which removes dissolved gases, particulate matter and corrosives from water and to a novel deaerator for use in such a water conditioning system. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in conjunction with an electrical power generator of the fuel cell type. Present commercial fuel cell power generators employ acid type fuel cells to which are delivered, as the reactant gases, air and hydrogen. As a consequence of the electrochemical reaction within the fuel cell, electricity and water are produced. The hydrogen fuel for the fuel cell power plant is, in a typical installation, produced in a commercially available subsystem known as a reformer by the reaction of water, in the form of steam, and a reformable hydrocarbon fuel such as natural gas. The water employed to generate the steam used in the reformer should be very clean and preferably should be free from dissolved carbon dioxide, carbon monoxide, nitrogen, chlorine and oxygen. This "feed" water should also be free of hydrogen sulfide, organics, particulate matter and many minerals. The presence of dissolved oxygen and carbon dioxide in feed water leads to boiler corrosion and the life of the steam generator of a fuel cell power plant can be maximized by use of feed water which is free from these dissolved gases. Similarly, any minerals which might deposit on the boiler heat transfer surfaces and thus reduce the heat transfer rate should preferably be removed from the boiler feed water. Those materials which might not have a deleterious effect on the boiler, such as sulphur and chlorine, but which could cause poisoning of the catalyst in the reformer should also be removed from the feed water.
It is known in the art that the water used for producing steam for the reformer of a fuel cell power plant may be condensed out of the exhaust gases from the fuel cell stack. This is considered desirable because it provides for a closed loop system thereby increasing the total fuel cell power plant efficiency and eliminating the need for an external source of water. Since materials which could contaminate the reformer and possibly also the fuel cell may be brought into the system with "outside" water, a closed loop system offers the advantage of assuring a supply of pure boiler feed water.
The prior art fuel cell based power plant systems have not employed the water produced in the fuel cell as boiler feed water because a suitable water conditioning system was not available to remove contaminates therefrom so as to produce a sufficiently clean boiler feed in an economical manner. Thus, previous proposals for employing the water vapor laden fuel cell stack cathode exhaust gases as a source of reformer steam generator feed water either required equipment which, because of its expense, would render the entire fuel cell power plant economically unattractive and/or required the use of an excessive amount of fuel or of the generated electrical power.